Virtual reality can be viewed as a computer-generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display device that has near-eye display panels as lenses to display a virtual reality environment, which replaces the actual environment. Augmented reality, however, provides that a user can still see through the display lenses of the glasses or other wearable display device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as a part of the environment. Augmented reality can include any type of input such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that a user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality, from generation of the virtual objects and images so that they appear realistic in a real environment, to developing the optics small and precise enough for implementation with a wearable display device.
A challenge to the implementation of wearable display devices, such as a head-mounted display (HMD), for augmented reality is maintaining the alignment of the two, independent left display lens system and right display lens system of a wearable display device. For binocular viewing systems, such as a wearable display device (e.g., glasses or a head-mounted display), the left and right display lens systems generate independent images of the same view. If the left and right display lens systems are not properly aligned so that the left and right images are projected directly one over the other, then the user's view will appear blurry. This is particularly noticeable for a vertical misalignment of the images, whereas a person's eyes can adjust to correct for a minor horizontal misalignment of the images. A conventional approach is to utilize a bulky and cumbersome opto-mechanical alignment system.